Fishing for brighter lights

CINCINNATI, Ohio – What happens when LEDs become waste? They’re not biodegradable and so will sit around in landfills, taking up space and possibly contaminating the ground around them with nonbio-based materials. A professor at the University of Cincinnati is working with what could be the most bio-based material of all in the fabrication of organic LEDs (OLEDs).

Salmon DNA or, to be more exact, salmon sperm, is being used as an electron-blocking layer and has been found to be one to two orders of magnitude more efficient than traditional materials, such as gallium arsenide and gallium nitride. According to Andrew Steckl, an Ohio Eminent Scholar and member of the university’s department of electrical and computer engineering, the researchers chose salmon sperm not only because it is very rich in DNA but also because it’s a waste product of the fishing industry. The work is being done in conjunction with the US Air Force Research Laboratory in Colorado Springs, Colo., which had been working with DNA for other applications and had a great source of salmon sperm in northern Japan.

A conventional structure

The design of the OLEDs uses a “more or less conventional structure,” according to Steckl, but when the investigators added DNA as an electron-blocking layer, they saw a significant improvement in efficiency. One of the challenges of working with DNA is that, as a complex polymer, it bends and takes on complex shapes. “It can be like a ball of twine that cats play with,” Steckl said. DNA is usually studied in a wet medium, such as in biomedical work, where wet is its natural ambient environment. “That’s not as useful if you want to know how it operates in devices,” he explained. In the process of “casting about for ways to make fine line structures,” the researchers realized that DNA changes significantly when exposed to radiation.

Salmon DNA, gathered from waste products from the fishing industry, is used as an electron-blocking layer in an OLED design. They successfully applied electron beam lithography using a direct-write method, allowing them to bypass many traditional steps. What they have achieved so far is not only the first use of direct-write electron beam lithography patterning of DNA-based materials (described in the Journal of Vacuum Science & Technology B, November/December 2008) but also efficiency using a truly “green” material. The next step is to figure out how to make very small structures and to look at how charges move through them and how photons are emitted.

They’re also looking at using DNA in electrically pumped lasers. They’ve found that they can make an optically pumped laser using DNA and lumiphores, “but to make an electrically pumped laser is a lot harder and a lot more useful,” Steckl contends, “because you have to understand how the current passes through the DNA.”

The effect that this work can have on the environment is unquestionable. DNA or similar polymers are naturally renewable materials that are abundantly available at low cost. They’re also biodegradable, so at the end of an OLED’s life cycle, there would be no environmental damage. When asked if they’re studying other forms of DNA or other organic materials, Steckl said they have their hands full with the variables involved with this material and have to take many steps forward before examining other nature-based materials. So for now, salmon sperm it is.